There is a bit of debate who is more likely to shut down below. I can't answer than myself but if Google did shutdown Drive it would likely be because they want out of the market and would give a long warning. If Dropbox left the market it would probably be because they can't afford to keep the doors open and may close in a hurry if this did happen.

Either way I like the competition and whichever one has better security would be my preference. But in terms of shutting down I think it's important to consider how they would shut down if they did, as much as 'if they would'.